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Java: download & install on Linux

[last updated: 2019-05-23]

go to: Java
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This page is a record of everything I did, including what didn't work.
If you want the short version that worked, go here:

(go to:) Successful Java Install on Linux

Everything below here is just a record of things that didn't work and can be ignored.
[FORMATTING ON THIS PAGE IS NOT CLEANED...]
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  • link to: wikiHow
    • This method did not work and was abandoned...
    • under Method 1: Installing on Non-RPM Linux,
      click "Java for Linux Download page"
      link to: download Java for Linux
    • At the bottom of the colored box, click: jdk.java.net
    • At "Ready for Use" click "JDK 12"
      This will download the Openjdk release
    • At JDK 12.0.1 General Availability Release page
      under Builds - Linux/x64, click tar.gz
      select "Open with ..." Archive Manager (default), click OK
      wait ...
    • Dialogue box opens, with filename at top, labeled [read only]
      At this point, instructions in the wikiHow diverge from what I'm seeing.
      Instructions say I should have a filename of the form "jre-8uxxx"
      but my filename is jdk...
      Best guess at this point is that these instructions are written for full version,
      while I'm attempting to install the free OpenJDK version.
    • Abandoning this path
    Top

  • link to: Instructions for downloading and installing JRE - Java Runtime Environment"
    JDK is a superset of JRE, and contains everything that JRE contains, plus other stuff.
    Bottom line, since I'm installing JDK, I don't need JRE.

  • Another attempt:
    • Since java will be installed in usr/java, and there was no such directory, I created one with $sudo mkdir.
    • Downloaded the openjdk...tar.gz into Downloads folder.
    • Used sudo mv to move it into the usr/java folder.
    • link to: these instructions
      say to unpack the .gz with this:
      $ tar xvf openjdk-12*_bin.tar.gz
    • Amazing - it seems to have worked. Everything was extracted into a new folder: jdk-12.0.1
    • $ java -version returns:
      openjdk version "1.8.0_191"
      OpenJDK Runtime Environment (build 1.8.0_191-8u191-b12-2ubuntu0.16.04.1-b12)
      OpenJDK 64-Bit Server VM (build 25.191-b12, mixed mode)

    • This tutorial for Beginners from guru99
      Great installation notes, as well as instructions for actually using Java:
      • Specifically:
        After successful installation, as evidenced by $ java -version,
        use text editor to write a Java program, save as [filename].java
        Then compile it ...
        But first, must set System variables in profile.
        • $ sudo nano /etc/profile
        • add these lines to the end of the file:
          JAVA_HOME=/usr/java/jdk-12.0.1
          PATH=$PATH:$HOME/bin:$JAVA_HOME/bin
          export JAVA_HOME
          export PATH
          ctrl-o to write/save, then press enter
          ctrl-x to exit
        • $ . /etc/profile to reload profile
        • ... now compile it with $ javac [filename].java
          This creates a file named as the name of the class that you've defined in your program, and has a .class extension
        • Then this file is executed with $ java [fileClassName]
        • However when I did this, I got an error...
        Top
      • Actual error (key things at least...):
        JNI error has occurred
        UnsupportedClassVersionError
        "A" (name of my compiled file, = name of the class that was defined in ... .java)
            has been compiled by a more recent version of JRE
        "A" was compiled with version 56.0, but this version of JRE only recognizes class file versions up to 52.0
        ...
      • ...now searching forums and hacking through to a solution...
        • maybe try uninstalling Java 12.0 and instead install 8?
        • This forum note says:
          Java SE 12 = 56
          Java SE 8 = 52
          and further suggests "either run the Java code with a newer version of Java JRE, or specify the target parameter to the Java compiler to instruct the compiler to create code compatible with earlier Java versions." with code snippet offered...
        • Another attempt:
          • Did apt-get update & dist-upgrade
          • $ dpkgs --list
            does not show JDK12 (however I forgot to look in the very long list for openjdk...)
            Best guess is that the back-door method I used to install it (downloading the tar and unpacking)
            was not best/proper way to install it
          • Intention is to uninstall JDK 12, and install JDK 8 instead.
            However as above, JDK 12 is not listed with dpkg command,
            so I can't use apt-get to uninstall,
            so I will uninstall the same way I installed it,
            manually deleting the files I copied in,
            as well as the usr/java directory I created
          • Then to install:
            $ sudo apt-get install openjdk-8-jdk
          • It seemed to work, however it did not re-create the usr/java directory...
            OTOH openjdk is listed in dpkg list
          • I discovered that, since I was in the /etc directory when I did the apt-get install,
            that's where it put the java-8-openjdk directory.
            OTOH that's not where I want it, so I manually moved it
            to the /usr/java directory that I created
          • Amazingly, it all worked. Test Java with 'Hello World'
      • ...




      eof

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